Electronic indicating system



Oct. 1, 1940. GEORGE 2,216,7Q7

ELECTRONIC INDICAIING SYSTEM Filed March 30, 1958 5 Sheets-Sheet lSUPPLY PLATE VOL7A6E FOR TRANSMITTERS 5 0R TRIPP/N6 VOLTAGE FOR 6.455005D/5CHAR6E TUBES.

AC SUPPLY INVENTOR. ROSCOE H. 6EORGE W ATTORNEY.

R. Hf GEORGE new, 1940.

ELECTRONIC INDICATING SYSTEM 3 Sheets-Sheei 2 Filed March 30, 1958 v cmWNW R Y B w I w $8? QQ w r Wm vm V M II M ME an: .0 u N g wfi J M m m vv3 n o m Q r\ n V V \mw .wm &

Oct. 1, 1940. R. H. GEORGE ELECTRONIC mmcmme sYs'rEM Filed March so,l938 3 Sheets-Sheet 3 R. m E m fg 5% ?05 H. GEORGE ATTORNEY.

Patented 1; 1940 FlCE Claims.

The present invention relates to a system for transmitting image signalsor characteristic indications of particular conditions obtaining at asignificant area being approached. In its more .8 specific form theinvention provides a system for transmitting indications such, forexample, as boundary lines, predetermined points or selected areas, orthe like on a significant surface which is being approached by anairplane, for example,

no or by a ship. Such a significant surface or area then may representan airport or some selected runway determined by wind conditions, forexample, upon which the airplane is to he landed or an area over whichthe airplane should fly in approaching an airport or the significantarea may be a harbor into which a ship is to be guided throughconditions of heavy fog or storm, for example. Since problems ofairplane and ship navigation are generally similar, and the former the 3more diflicult, particular reference is made herein to the applicationof this invention to airplane guiding although it is to be appreciatedthat there is no restriction of scope intended by such reference.

The problem of transmitting actual images of landing fields andsurrounding objects to pilots attempting to land aircraft on fog orstorm obsoured fields or to guide ships into harbors under. similaradverse conditions is greatly complicated by the necessity that the viewtransmitted must be that which the pilot would see if the airport orharbor were visible to the eye. Hence, if such forms of transmission areto be useful to any great degree, it is almost essential that the exactbearing of the airplane relative to the landing field or airport shallbe known. During periods oi fog and storm, as well as during periods ofdarkness and heavy weather when the visibility is very limited, theairplane pilot in approaching the airport or the pilot guiding the shipis frequently unable to see the landing field or to sense the directionof the runways thereon until the aircraft is almost immediately upon thelanding field or the ship is outside the desired channel insofar asactual geographical separation is concerned, or until the aircraft isalmost upon the airport insofar as the altitude of flying is concerned.

Any method of transmitting the correct view of the field or airport to apilot by television would require not only a television receiver in theairplane where such receiver would usually embody ior good receptionwith adequate detail a substantial number of parts and a considerableamount of space, as well as expense of installation, but which wouldrequire also ground transmitting apparatus for accurately determiningthe exact position and direction of flight of the plane at all times,together with apparatus for rapidly selecting the correct image to betransmitted. It

is, of course, readily realized that systems of television of such anature wouldbereasonably certain to make safer airplane flights in badweather, in darkness, and at times landing fields are obscured byconditions of weather and the like, but it also is easily realized thatas a general proposition, such forms of apparatus are somewhatcomplicated for practical use unless the reproduced images which thepilot observes are so lacking any substantial detail that littleadvantage from a practical view point can be obtained.

Therefore, the present invention provides ways and means by which theindications of markers or special identification points or relativelocations of significant areas on the landing field are made to appearon a viewing screen or target, preferably located in the pilot's cabinoi the airplane, in correct perspective as points of light which arecaused to'appear before the pilot in substantially the same perspectiveas'he would actually see such points of areas were he able actually toview them.

A system of this nature preferably comprises on the aircraft two pairsof direction finding loops or directional receiving antennae andassociated circuits, that is, one for the horizontal direction and onefor the vertical direction, with suitable amplifiers connected to form apart of the receiving circuits. These receiving circuits are suitablyarranged for feeding the output energyinto bridge circuits from whichpotentials are developed to control the reproduction of the producedpoints of light. At the same time, through a suitable system ofbalancing the bridge circuit may be caused to operate and control asensitive automatic volume control to establish the desired level ofresponse of the system.

In the presently proposed apparatus the light point reproduction isinitiated as the production of light spots on the luminescent screen,target, or endwall of a cathode ray tube. Accordingly, the potentialsdeveloped at suitably selected points on the bridge circuit are appliedto control directly the electrical potentials applied to the electronbeam deflecting plates of an electrostatically deflected beam within acathode ray tube or the developed potentials are caused to control insuitable manner the current flowing through deflecting coils so as todeflect the electron beam in the electromagnetic type of beam deflectionsystem as used with present day cathode ray tubes. According to eitherform of system the electron beam developed within the cathode ray tubeis caused to impinge at difierent points on the luminescent screen ortarget in accordance with the magnitude of the potentials applied to thedeflecting plate electrodes or in accordance with the magnitude of thecurrents caused to flow through the electron beam deflecting coilsassociated with the cathode ray tube.

The circuits which are to accomplish this result are so arranged thatthey cause such deflection of the cathode ray beam that it indicates onthe viewing screen of the cathode ray tube the amount of deviation ofthe aircraft from a position at which the aircraft should be moving orapproaching if flying directly toward the significant points or markersfrom which the radiant energy transmission originated. Thus, thetransmitting areas or markers are indicated on the observation target orscreen as several selected points on the significant surface beingapproached by the aircraft. The receiving circuits are provided withsuitable automatic volume control arrangements, as above suggested, tomake the receiver apparatus sensitive substantially only to the angle ofdeviation of the receiver relative to the transmitter rather than to theactual signal intensity being received upon the directionally responsivecircuits. As a general rule,and especially where a saving in weight isimportant, an electrostatic deflection control of the cathode ray in thelight point producing means is usually desirable, since the weight ofmagnetic yokes and some additional tubes usually required in theelectromagnetic systems are avoided.

Insofar as the transmission end of the system is concerned, a suitablenumber of radio transmitters are set up to mark the airport and therunways or the area over which the airplane is to be guided. Duringtransmission periods each transmitter is properly tuned to the samefrequency and arranged to be operated sequentially and successively forshort time periods, for example, time periods of the order of ,6 of asecond so that with a system from which six separate transmitters sendout signalling indications, each transmitter representing the locationof one of the suggested six significant markers on the sig nificantsurface will be operated once each 20th of a second. Assuming thetransmission is thus carried on and the receiver is operated as abovedescribed the positions of impact on the screen or target area by thecathode ray beam. developed within the receiving tube which is locatedwithin the field of view of the airplane pilot will indicate as a seriesof points the several transmitter locations. Thus, the position of theairplane with respect to each of the several significant markers of theairport or of the area over which the airplane is to be guided duringthe period of operation of the transmission is readily discemible.

As a result of the rapid repetitions of a series of points indicatingthe location of each marker on the significant surface, the pilot wouldobserve on the viewing screen or target area of the cathode ray tube abright spot for each marker on the airport or the area over which theplane is to travel. At all times the position of these several brightspots on the viewing screen of the cathode ray tube is caused to appearin correct perspective since each reading or light spot production pointis corrected at least twenty times per second so that the observedeffect corresponds to that view which the pilot would actually see werebe able to-look through a hole in the instrument panel at lights locatedat positions on the airport or significant surface corresponding to thelocation of the several radio transmitter positions. The airplane pilotthen by watching his meters registering altitude while making hisobservations of location relative to the significant area is easily ableto make a safe landing in fog in the same manner as he would be able toland were he able to see marking lights on the airport and runway intrue visual perspective as he approached the field.

Further, as a part of the present invention provision is made totransmit from the airport at each of the selected significant points ahorizontally polarized wave for the horizontal direction findingapparatus and a vertically polarized wave for the vertical directionfinding apparatus in accordance with the suggestion above that thereceiver equipment on the airplane comprise two direction findingcircuits, that is, one for horizontal and one for vertical directionfinding. Suitable provision is made at the airport from which thetransmission to the airplane take place for switching in sequencebetween each of the several transmitters for this purpose, and, accord:ingly, during the period of persistence of vision, herein assumed asone-twentieth of a second for illustration, each transmitter isenergized at least once.

A further provision of the present invention is that of developing asystem for guiding an aircraft or the like so that the aircraft is ableto follow a series of marking points or locations so as to fly along apredetermined course with the greatest possible security irrespective ofweather conditions. For example, if the airplane is to be guided througha mountainous region and is required to fly through certain passes inthe mountains, it is possible by the arrangement of several transmitterswhich radiate energy according to a predetermined sequence to observe onthe indicating tube 01' the receiver equipment located on the airplanepoint representations allocated in space in the same relative locationas the actual transmitters. Under such conditions, for instance, if thelocation point reproducing device, such as the cathode ray tube, is sodivided or marked that a dividing line is drawn through its center in ahorizontal direction, this dividing line will represent to the pilot thehorizon. In order that the elevation of the airplane may be maintainedthe pilot will so guide the ship that all of the several points to beindicated along a straight line path appear on the observation screen atlocations slightly below the center dividing line. In order that thepilot may know that he is following exactly the proper course of theseveral points reproduced to represent the relative location of thetransmitting points, he will guide the plane so that all of the severalpoints also appear approximately in the center of the tube as regards avertical line through the center.

In some instances, it is desirable also, in flying through mountainousregions, to provide for transmissions from bounding locations marked ateither side of the several transmitters located according to thedirection of flight and in addition thereto. These transmitters also arearranged to radiate energy at the same frequency as those to mark theline of flight but in order that the point designations produced on thereproducing device to represent the course followed may not, by chance,be mistaken for actually the guiding points, it is usually desirablethat the repetition frequency of these limited locations be atsubstantially reduced rate in order that the point designations producedon the viewing device may occur more infrequently and the pilot may beable to sense at once that the infrequent designations are pictorialindications showing the limits within which he must maintain his course.In such a case, it is, of course, easy to control the line of flight bythe line of flight indicating radiations and the auxiliary guide pointsmay even be represented upon the screen as points of greater elevationthan that at which it is necessary to maintain flight and thus theauxiliary points may appear on the screen either above, below or at thesame level as the line of flight control indi-' cations'but spacedlaterally apart therefrom.

In accordance with the above mentioned gen eral characteristics of theinvention to be herein described, it is an object of the presentinvention to provide a simplified form of transmitting and receivingequipment which shall be capable of functioning to guide and directairplanes to airports or ships into harbors in such a manner that theairplane may approach the landing field or airport or the ship enter aharbor in total darkness (or blind" so-to-spealg) or in bad weatherconditions with substantially the same degree of safety as if thelanding port or field or the harbor were completely visible to thepilot.

A further object of the invention to be herein'described is to provide ameans for guiding aircraft, ships or the like which is relatively simplein its construction and arrangement and to provide a system wherein theemcient results of visual transmission of a significant surface isaccomplished through the mere transmission of certain selectedsignificant points on that surface.

A further object of the invention is to provide ways and means forguiding aircraft and the like wherein the receiver equipment providesfor the viewing of certain selected significant points of a significantsurface in true perspective in order that the pilot may be able to guidehis craft toward the significant surface under all conditions ofweather, darkness and the like.

Still a further object of the invention herein set forth is that ofproviding a system of indication either for portraying a significantarea or for indicating a course of travel or the like which will producea series of point indications which appear in substantially actualperspective and free to move over the indicating device to difierentpositions thereon so as to represent effectively relative locations. Insuch event the central portion. of the indicating device, as regards thevertical line therethrough, will represent that area which is directlyin the line of travel and the center as regards the horizontal linetherethrough will indicate substantially the level at which flight isbeing maintained. Other systems heretofore proposed have suggested thatseveral point indications on a viewing tube, such as a cathode ray tube,may be produced where the point indications appear along a radius andthe separation between various points indicates the relative distancefrom the area or markers. however, do not portray the true perspectiveof the indicated markers and, in most instances, with such systems ofthe prior art in order to obtain indication of both horizontal andvertical positions with respect to the significant points require twoseparating indicating devices in contrast to the single indicatingdevice herein proposed.

An additional object is to provide a transmission system which willprovide visible guiding indications'and yet be so simple in arrangementas to be operated without any substantial degree of attention. It is astill further object of the invention to provide receiving equipmentwhich is so light in weight, due to simplified circuits and a limitednumber of constituent parts, as to enable it to be used on substantiallyall aircraft without fear of adding sufiicient weight to require eithera reduction in the so-called pay load or Such systems,

ply carried by reason of added weight due toauxiliary equipment.

As a still further object of the invention provisions may be made forinstallations of the transmitter arrangements in such manner that theairplane may be guided over treacherous country, such as through a passbetween mountains, by means of the indications observed, although thereis no attempt actually to land the airplane on the significant surfaceor area from which the guiding indications are radiated. This form alsoapplies particularly in guiding ships through narrow and treacherouschannels or 'harbor entrances. Hence, the invention has wide applicationto directional course guiding even though there is no attempt, as inaerial navigation, to

land an airplane within the area from which the radiationsoriginate.Thus, the transmitter arrangements to be described herein may be used,

where desired, as replacements for the usual beam markers along airways.

Still other objects and advantages of the invention will immediatelybecome apparent and at once suggest themselvesto those skilled in theart by reading the specification to which it is directed and by theaccompanying drawings wherein:

Fig. 1 represents schematically one of the several runways at thelanding field and also represents in a diagrammatic manner the locationof the several transmitters at selected significant points on asignificant area which are so arranged that each transmitter maytransmit both horizontally and vertically polarized waves of radiantenergy; and, in addition, the figure also indicates schematically onearrangement for switching sequentially between the several transmittersso that each may send radiations of energy at desired time periods;

Fig. 2 is a schematic representation of an arrangement of oscillator foruse with the transmitter at any or all of the several transmittingpoints shown by Fig. 1;

Fig. 3 diagrammatically represents one of a number of difierentalternative transmitter arrangements which may be used for the systemshown by Fig. 1;

Fig. 4 is a circuit diagram of one of several forms of receiverarrangements, it being understood that the receiver of Fig. 4 sincebeing of the heterodyne type is preferably used with the longerwavelength transmitted from the several transmitters of Fig. 1 andparticularly that form of transmitter shown by Fig. 3; it being hereinunderstood however that all of the wavelengths to which the systemherein described is primary, although not necessarily, adapted aresubstantially within the range known in the art as micro-waves and thusof the order of one meter or less in length; and,

Fig. 5 is a schematic representation to indicate schematically thegeneral arrangement of the antenna and reflector systems for radiatingboth vertically and horizontally polarized waves at each transmittingpoint and, at the same time, the arrangement of this form of theradiating means for practicing the invention is particularlycharacterized by its properties of directional and polarizedtransmission or radiation.

Referring now to the drawings and first to Fig. 1 thereof, the runway Iis conventionally represented as one of the several runways located atthe landing field or other significant area (not herein shown completefor simplification) toward to require any substantial reduction in fuelsupwhich the airplane is approaching. Positioned symmetrically withrespect to this runway are a number of transmitter stations 2, 3, 4, 5,6, and 1. Each of the transmitters is arranged to transmit a verticallypolarized wave by means of the vertical dipole antennae 8, 8 as well asa horizontally polarized wave by means of the horizontal dipole antennae9, 9' to which energy is supplied from the several transmitters by wayof the transmission lines H and V which are conventionally indicated butwhich in practice are each shielded within suitable shielding means suchas copper tubes.

Where directional transmission is desired, these several transmittingantennae may be provided with suitable reflectors, preferably arrangedbehind the antenna and projecting forward thereof in the direction ofwave propagation according to a parabolic arrangement. Reference may bemade to Fig. 5, later to be referred to more specifically, for anillustration and explanation of .one suitable manner of arranging thedipole radiators 8, 8' or 9, 9' or both with reflectors, but for thesake of simplicity this complete arrangement is not indicated by Fig. 1although it is to be understood that the arrangement of Fig. 5 may, andpreferably should, be incorporated with the system shown by Fig. 1.

If, now, an airplane is approaching the landing field and, for example,the wind direction across the landing field-surface is that shown by thearrow immediately above the runway I, it will be desirable for theairplane to land on the runway I in a direction so as to come into thewind. Accordingly, it will be assumed herein that the airplane isapproaching the landing field from a direction to the right of thetransmitters 4 and 5 in order that it may land into the wind and firstapproach the end ID of the runway and move toward the end II whenstopping. Under such conditions it is desirable, in

accordance with the above brief outline of conditions of operation, thatthe several transmitters 2 through 'I be controlled in sequence so thatenergy is radiated sequentially from each. In accordance with whateverenergy is radiated, point representations to indicate the relativelocation of the several transmitters 2 through I with respect to therunway I may be obtained on the viewed target or screen I25 of thecathode ray tube or its equivalent (see Fig. 4) located within the viewof the pilot. Further, as was above set forth as onecf the principles ofthis invention, such viewing of the several points from whichtransmission takes place is intended to be in substantially the sameperspective as these points would be seen by the pilot could he actuallyview the landing field.

Accordingly, each transmitter 2 through I is connected with somesuitable form of switching device, herein indicated conventionally as adistributor I2, by means of a separate conductor which, when energized,serves to control the operative period of each transmitter. As has beenshown herein conventionally, and for which fura power pack, batteries,tubes or any desired form of which only a few are herein suggested.

This source of applied voltage connected between the terminal points I5and I6 is fed through a contactor or brush I! to the inner ring I8 ofthe distributor I2. Attached to and electrically connected with theinner ring of the distributor I2 and rotating therewith at some suitablerate, for example to 30 times per second which coincides with the numberof times per second it is desired to transmit from each separatetransmitter 2 through I, is an electrically conducting contactsegment I9which, for the assumed case of six transmitters located adjacent to therunway I, will extend for an arcuate distance of" just slightly lessthan 60 degrees on the circumference if it is desired that the severaltransmitters operate sequentially but with no time overlap. I

As the contactor I8 is rotated by any suitable prime mover whichoperates at a constant rate (for example, a synchronous motor geared toturn the contactor at the desired rate), it sequentially contacts thebrushes 20, 2I, 22, 23, 24 and 25 which are connected respectively withthe transmitters 2 through I by way of the conductors 26, 21, 28, 29,and 3|. Thus, it can be seen that in accordance with the position of thecontacting segment I9 with respect to any of the brushes 20 through 25one of the several transmitters 2 through I will be energized withoperating voltage from the source connected between terminals I5 and I5.while all other transmitters will be de-energized because the onlyelectrical connection to the source I5, I6 is provided by contact withthe segment I9. Accordingly, the rate of sequential energization of theseveral transmitters 2 through I will be determined in accordance withthe rate of rotation of the distributor I2 and the rate at which thecontact segment I9 thereof comes beneath and forms electrical contactwith the several contacting brushes 20 through 25.

It will be appreciated that such arrangement for switching intooperation the several transmitters 2 through I, preferably bycontrolling the operative period of the oscillators thereof, as shownmore particularly by Fig. 2 later to be described, is, with thecontacting segment made to extend just slightly under 60 degrees asabove suggested, such that there will be no time overlap between theseveral transmitters. However, under some conditions it may be desirableto provide a very slight time overlap and under such conditions it ispossible to lengthen, so to speak, the

contacting segment I9 so that the energy supply from terminals I5, I6 isconnected for a minute portion of the 5 second operating time of eachtransmitter so as simultaneously to energize each of two transmitters.This could, for example, be provided by making the contact segment ofthe order of 62 degrees as contrasted to just slightly less than the 60degree segment.

Further than this, as has already been ex- "plained in U. S. Patent No.2,089,430, granted to ing oscillations at radio frequencies which may besent out from the radiating antennae or dipole sections 8, 8' and 9, 9'may be provided by a simplified form of oscillator arrangement such asthat shown by Fig. 2. In .such an arrangement the oscillator tube 32 isconnected substantially according to a form of electrical connectionswhich have been known in the art broadly as the Hartley type oscillator,although, obviously other forms of oscillators, such as the Collpitts,the Barkhausen Kurz or equivalent types, may be used. In thisarrangement the the oscillator tube 32 couples into the tankciroscillating frequency is determined by the general relationship ofthe inductance 33 serving as the primary of a transformer, which is tofeed power to the antenna sections 8, 3' and/or 9, 9' through thefeeder-line 46 considered together with the other main element of thetank circuit which is the usual condenser 34 (preferably variable). Theplate or anode element 35 of cuit comprising the inductance 33 and thecapacity 34 by way of the coupling or blocking condenser 36. Similarly,the grid or control electrode 36' is coupled into this same tank circuitby way of the grid leak and condenser combination 31. The cathodeelement 38 of the oscillator tube 32 is suitably energized from a sourceof alternating current (A. C. supply) through the transformer 39 and itssecondary in known manner or a direct current source may be used wheredesired. The ground point of the cathode 38 which is the center tap ofthe secondary winding of the transformer 39 connects to an intermediatepoint 40 on the inductance .33. Plate voltage for the oscillator issupplied through the radio frequency choke 8| from a suitable source ofpotential, indicated as' 3+, connected at the terminal point 42, whichterminal point 42 is to be understood as connected to one of the severalcontactors or brushes 20 through 25 of the distributor ring I? of Fig.l. Oscillations developed by the oscillator 32 are then fed from theinductance 33, serving as the transformer primary, to be supplied to anenergy pick-up coil G3, forming the secondary of a'transformer, to thefeeder line 65, as above explained.

Under the circumstances where the output energy of the oscillator 32 issufllciently large, it

is unnecessary to use independent oscillators for developing. the energyfor the vertically and the horizontally polarized energy to betransmitted from the antennae 8, 8 and 9, 9. Accordingly,

the vertical and the horizontal antennae for this arrangement may be fedwith energy 90 degrees out of phase with respect to each other by makingone pair of feeders 44, for example the feeder pair connecting with thehorizontal antenna, a quarter wavelength longer than the feeder pairwhich is to connect with the vertical antenna. In this manner. anappropriate control of the transmitted energy may be obtained. It shouldbe noted in this instance that the energy radiated from the vertical andhorizontal dipoles 8, 8' and 9, 9' is not modulated but merely keyed onand off by the distributor l2. Therefore, the receiver arrangement ofFig. 4 is particularly suited to receive the transmitted energy.However,

the invention is in no sense restricted to the transmission of anunmodulated and on-off keyed carrier and, accordingly, reference may bemade to Fig. 3 for a modification of a transmitter wherein modulation ofthe carrier energy is obtained.

Referring now .to Fig. 3, which is a schematic representation of onesuitable form of the transmitter wherein the carrier frequency energy ismodulated as above noted, there has been shown conventionally theoscillator arrangement which is to supply modulated energy to theradiators 8, 8 and 8, 9' more particularly shown by Fig. 5, which areenergized in a manner which will be more particularly explained laterherein. The transmitter of Fig. 3 is so constituted that the carrierenergy developed may be transmitted either modulated or unmodulated asdesired.

Usually, for use with greatly simplified receiver apparatus it isdesirable to transmit a modulated carrier for simplified receiverapparatus. In the ultra-short and micro-waves this becomes especiallydesirable with the necessity of extremely simplified apparatus becauseof weight limitations on airplanes and because extremely small pick-upapparatus is required where it is essential to reduce wind-drag ifproper cruising speeds are to be maintained. Accordingly, thesuper-heterodyne receiver frequently is not of optimum utility undersuch conditions, although as a general proposition, it is not at allcritical whether the carrier be modulated or unmodu lated.

In the form in which the transmitter has been shown by Fig. 3 there hasbeen provided a separate oscillator for each of the vertically ,andhorizontally polarized waves which are to be transmitted, although, aswas apparent from reference to Fig. 2 previously described, it is not atall essential that separate oscillators be provided if the power outputof one oscillator is adequate. However, in the form in which thetransmitter has been illustrated by Fig. 3, the oscillator tube 65 maybe assumed, for example, as serving and developing the carrier energyfor the horizontally polarized wave to be transmitted from the radiators9, 9' while the oscillator tube 46 develops carrier energy for thevertically polarized wave to be transmitted from the radiators 8, 8'.

The form in which the oscillators and 45 have been illustrated is aschematic representation of the general form of oscillator which may becharacterized as the resonant line type. In this form of arrangement,there has been connected to the anode or plate electrodes 41 of each ofthe oscillator tubes and Mi and to the control electrode or gridelements 48 of these tubes, parallel lines 59 and 50. These parallellines 49 and 50 are usually in the form of tubular conducting memberswhose length may be adjusted the operating parameters. In thearrangement herein shown operating potentials are applied to the anodeor plate electrodes 31 of the tubes 45 and 66 by way of ajconductor 5|which is energized in accordance with the operative conditions of a tube52, later to be described. The

control electrodes or grids 44 of the tubes 45 and 48 are supplied withsuitable operating bias by means of the self-biasing arrangementprovided by way of the grid leak and condenser combinaheating currentsto the emitters or cathodes 55- of the tubes 45 and 46 pass throughsuitable copper tubes 6| which are preferably of a length equal tosubstantially one-quarter of the wavelength of the carrier frequencyoscillations to be developed. The copper tubing 6| is preferablygrounded, as shown, through a suitable condenser 62 and in the cm of thecopper tubing into which the leads 56 and 51 enter and connect to thetransformer winding 58 there is provided an adjustable plug 63 whichslides in and out of the copper tubing 6| in such a manner as to provide an electrical connection between the inner conductor 56 or 51 andouter shell portions of the copper tubing. By suitably positioning theadjustable plugs 63 within the copper tubing 6| the effective length ofthe combination may be suitably adjusted so as thereby to be madesubstantially the one-quarter wavelength long, as above mentioned.

Thus, with suitable anode or plate voltage supplied to the oscillators45 and 46, which oscillator tubes may be for example by way of referencebut not in any limiting sense of the general type known in the art asthe Western Electric type 316-A tube, will provide for the developmentof electrical oscillations of a frequency determinable by the length ofthe resonant lines 49 and 50. I

In order to supply these developed oscillations to the radiating antennamembers or dipoles 8, 8' and 9. 9' a suitable feeder line is coupledinductively by the loop 64 to the members 49 with the point of couplingbeing closely adjacent to point 65 from which the line member 49 isconnected to A. C. ground through the condenser 66, which point 65 isthe point at which plate voltage is supplied to the anode members 41 ofthe oscillators 45 and 49.

The transmission line 61 to which each inductive member 64 is connectedfeeds the energy developed by the oscillators to the antenna or dipolesections 8, 8' and 9, 9' (see Fig. 1). Under usual operating conditionsthe antenna impedance for the dipole shown by Figs. 1 and 5 is of theorder of 72 ohms and, consequently, the transmission line 61 is sodesigned that its impedance is likewise of the order of v'12 ohms sothat standing waves are then substantially nonexistent along the line.However, it is contemplated for this invention that the resonant linetype of transmission may also be used where desired and it should,therefore, be understood that voltage for the oscillators 45 and 46 wassupplied by way of the current flowing through the tube 52. This tube52, which is preferably a grid controlled gaseous discharge type, hasits plate electrode 40 energized with alternating current fed throughsecondary winding 4! of the transformer 59 so that with the supplyvoltage at the terminals 60 being 60 cycle alternating current the plateor anode electrode ll becomes positive 60 times a second and for A of asecond duration each time. This application of positive voltage duringthe positive half of each cycle of the supply energy would cause thistube normally to draw plate current in the absence of any bias upon thecontrol electrode 10 of the tube serving to overcome the positivepotential in the anode or plate 08 acting in such a manner as to causethe tube to remain biased to cut-off. The tube 52 is preferably,although not necessarily, a gaseous discharge tube provided with acontrol electrode and may .be, for example, a tube of the type known inthe art as the Thyratron or a tube of the type known in the art and soldunder the identifying nomenclature GE FG-l'l.

The heater current for heating the cathode II of the tube 52 is suppliedin the usual manner by connection with the transformer secondary winding12. As shown, the :biasing source II is poled negative relative to thecontrol electrode II and with the 60 cycle A. C. from thesupply energysource connected to'terminals 4. fed also upon the control electrode IIIby way of transformer secondary l4 and the transformer I! after havingpassed through the resistor Ii it can be seen that the polarity of thealternating current supplied on the control electrode II is opposite insign to that upon the anode orplate element 44. In this way, tube 52 isalways at cut-off unless some provision is made, during the positivehalf cycle of the A. C. upon the plate .8, for overcoming the negativebias on the control electrode I0 so that the tube 52 can, draw platecurrent.

To accomplish this purpose there is connected at terminal point llcontacted by the switch arm 11' a contactor or distributor substantiallylike that shown at l2 by Fig. 1. In such event the lead 18 willcorrespond to any of the conductors 26 to 3| of Fig. 1 and at theterminals II and II of the contactor used under these conditions tocontrol grid voltage on the control element 10 (rather than to controlplate or anode voltage as suggested by Fig; 1). By feeding A. C. in thesame phase and frequency as the A. C. supplied to the anode 68 betweenthe terminals I! and II and of a polarity corresponding to that suppliedto the anode 68, it can readily be appreciated that the tube 52 will,with a six segment distributor of Fig. l rotating at the above assumed20 revolution per second rate, become conducting upon every third cycleof the alternating current supply connected at the terminals 40. Also,in this connection it should be noted that with such an arrangementalternate transmitters should be connected in reverse phase so as tobecome operatlve at the proper time, that is, for example and accordingto the above assumed order of operation, the transmitters 2, 4 and 6are-connected to operate out of phase with respect to the transmitters3, 5 and I insofar as phase is related to the 60 cycle A. 0. supplyenergy. Thus, whenever tube 52 draws plate current and, as aboveexplained, during one-half of every third cycle of the A. C. supply withsix transmitters anode voltage for the oscillator tubes 45 and 40 issupplied through tube 52 by way of the conductor 5|.

Where it is desired to modulate the oscillators 46 and 66 there may alsobe provided a push-pull oscillator tube 38, such as a tube of the typeknown in the art as RCA type 53. This tube 88 also has the heaterelement for the cathode 89 energized from the secondary winding I2 ofthe transformer 59 and the grid or control electrodes 96 and 9B connectthrough resistors 9|, 9!, to the end terminals of the secondary windingof transformer 92 which secondary is preferably grounded in itsmidpoint, as indicated. The output or anode elements 93 and 98' of thetube 88, connect respectively to the end terminals of the primarywinding of transformer 92 to the center point of which anode or platevoltage for the tube 88 is supplied by way of the conductor so throughthe resistor 95. This anode voltage is supplied either from the platevoltage supply in the distributor ring I? of Fig. l, or through the tube52 of the hereinabove described arrangement to supply anode voltage forthe oscillator tubes 65 and as.

Across the primary and secondary windings of the transformer 92 thereappears, naturally, oertain distributed capacity, conventionallyillustrated, so that to develop oscillations for modulating theoscillators 65 and $8 at the desired frequency, for which a frequency of6000 cycles may be assumed as illustrative, no additional capacity needbe added.

The oscillations developed in the push-pull oscillator tube 88 are thenfed to the half-wave rectifier tubes 98 and 97 and, in accordance withthe'rectlfied output from tubes 96 and 9! representing alternate halfcycles of the developed oscillations the resultant energy is supplied byway of conductors 98 and 99 to the grid or control electrodes 3% of theoscillator tubes 65 and 46 so as to modulate these oscillators at thefrequency developed by the oscillator 88.

The voltage supplied by way of conductors 98 and 99 from the diodes 96and 97 to the oscillators 65 and 66 respectively serves to add to thebias applied to the control electrodes 68 of the last named oscillatorsand accordingly the ap- 5 plied potentials thus adding to the biasalready supplied by the self-bias arrangement comprising the grid leakand condenser combination 53, 6Q which bias these tubes for alternatehalf cycles of the frequency developed by the oscillator 88 negative tocut-oil, in which event plate current ceases to flow through theoscillators 55 and d6 during the periods when current fiows through thehalf-wave rectifiers 9t and 91 respectively. Where no modulation of theoscillators t5 and 66 is desired the switch I may be opened in orderthat the oscillator tube 88 shall never receive plate voltage and henceshall remain inoperative at all times during opened condition of theswitch I60.

From the foregoing it can be seen that the ground apparatus consistsessentially of boundary and runway markers in the form of small radiotransmitters arranged to be operated one at a time in rapid successionand preferably all transmitters operate on the same frequency. This isespecially desirable in order to simplify the receiving equipment which,as above mentioned, is located on the airplane approaching the landingfield or .being guided over certain territory where no landing isdesired or, for instance, used upon the boats entering into the harbors.

Making further reference now to the receiver equipment which is to belocated upon the airplane, that equipment preferably consistsessentially of two pairs of loop antenna such as is used with the homingindicator or'directional aerials. In addition, and in combination withthe receiver equipment, there are provided special automatic volumecontrol amplifiers which are arranged to feed into bridge circuits forobtaining so-called plus and minus readings when the airplane is notflying directly toward the operating transmitter. With this arrangementoneof the pairs of loops and its. associated amplifier would showhorizontal deviation while the other of the pair.

of loops and the associated amplifier would show vertical deviation. Ifnow the horizontal deviation potential is applied to the horizontaldeflecting plate electrodes of a cathode ray tube in which the deflectedcathode ray beam is to be deflected electrostatically and the verticaldeviation potential is applied to the vertical pair of deflecting plateelectrodes of the same tube, then it is apparent that the point ofimpact of the deflected cathode ray upon the target or luminescentscreen would be a spot on that target or screen corresponding to theposition of the operating transmitter with respect to the airplane. Ifthe amplifiers of the receiver and the receiving loops are sensitiveonly to angle and not to changes in signal intensity, the cathode raybeam itself being practically free of inertia can register rapidly thereadings from each of the transmitters as they operate in rapidsuccession. If now each of the transmitters is operated once every 20thof a second, this being assumed to be a frequency higher than therequired frequency. to maintain persistence of vision, and if it beassumed that the target or luminescent screen has a reasonably long timedelay. characteristic, then points of light resulting from the impact ofthe electron beam upon the screen or target of the cathode ray tube willappear. The pilot is then able to observe spots of light located in thesame relative positions as the transmitters at the landing field wouldappear were he able to look through the instrument panel at lightslocated in the same relative positions as the transmitters.

Also, it will be appreciated that with the sev= eral transmitters at thelanding field or over.

areas where the plane is to be guided and where each transmitter isarranged to transmit energy once each 20th of a second or so, it isapparent that the readings will produce luminous spots observable on thetarget area of the cathode ray receiver tube and that these visual spotsand the locations thereof upon the target area will be corrected each20th of a second as the airplane approaches the landing field. Thus, theproduced luminous spots actually move across the target or screen areaof the viewing tube in their true perspective.

With these thoughts in mind, reference may now be made to Fig. 4 of thedrawings'which shows by way of example one suitable form of receiverarrangement wherein two loops are indicated .by way of example forreceiving the transmitted horizontally polarized waves and two similarloops are utilized for receiving the transmitted vertically polarizedwaves. Since the circuits connected for receiving the horizontally' Inthis receiver shown by Fig.4 the loops IOI and 20I are arranged toreceive the transmitted horizontally polarized waves and these loops maybe orientated in known manner. Usually, when the loops'are properlyorientated with respect to the ship or airplane they are flxed inposition and only the orientation of the ship or airplane with respectto the transmitters aflects the indications on the cathode ray tube. Theloops IM and 20I are suitably tuned by means of the variable condensersI02, 202, and are caused to supply the received energy to the No. 4 gridI03, 200 of the modulated oscillators I04, 204, which are also known inthe art as pentagrid converters. The oscillators I04, 204 are connectedas push-pull oscillators with the No. 2 grids I05, 205, serving as theplate electrodes and the No. 1 grid I05, 205' serving as the controlelectrodes. Connected with the No. 2 grid I05, 205 which is to servesame plate electrode of the oscillator is the usual form of tank circuitcomprising the.

l is provided by way of the blocking. or coupling condenser H and 2I0,which with the usual resistors III, 2 connected to ground, provide aself-biasing arrangement for the oscillators.

The resultant oscillations developed in that portion of the oscillatormodulator I04, 204 bequencies through the transformer couplings II2,'

2I2 to the intermediate frequency amplifiers H3 and 2I3, as indicated.

The modulated oscillators I04 and 204 are preferably the super controltype mixer tubes and it is recommended that a tube operating in thiscircuit with characteristics closely analogous to those of a variable mutype tube be used, and such tubes as those known in the art as the GA?or 6A8, or an equivalent type tube having similar characteristics, haveproven satisfactory.

The intermediate frequency amplifiers I I3, 2I3, are preferably of thetype tubesknown in the art as the type 58 or the 6K7 although, ofcourse, other tubes may be used where desired. Amplifled intermediatefrequency oscillations appearing in the output circuit of the tubes H3and 2I3 are fed by way of the coupling transformer H4 and 2 to thedouble diode rectifier II5 for example, a tube of the general type knownas the 6H6 and applied between the anode electrodes I I6 and 2I6 thereofand ground at I".

While not previously mentioned herein it should with the direction ofthe transmission or, as

above explained, when the loops are fixed after proper orientation theorientation of the airplane or ship with respect to the transmitters isestablished. The output energy from the double diode II5 which flowsthrough the resistors I20 and 220 to ground at 22! via the commonresistor I22 connected to the junction point of the output resistorsI20, 220 should be'constant and thus the potential at the junction pointI23 oi the output resistors for signals received by the -loops IOI and20I, will be a predetermined value above ground 22I measuredinaccordance with the drop taking place through the resistor I22. Thus,there is formed by means of the combination or the several resistorsI20, 220 and I22 a bridge arrangement so that in accordance withvariances of current flowing through resistors I20 and 220 the potentialat the point I23 will shift to varying values above that of the groundedend of resistor I22. Such potential is determined in accordance with thesignal strength received upon the receiving loops.

It can also be appreciated that with the output oi! each portion of thedouble diode II5 connected to opposite deflecting electrodes or platesI24 and 224, which are assumed to constitute the upper deflecting platepair, of the cathode ray tube (conventionally indicated) that theelectron beam passing from the electron gun structure I20 toward thetarget or screen I25 and passing between these plates during its travelwill be deflected from its normal path in accordance with the differencein voltages between the outer ends of resistors I20 and 220 and ground22I which are applied to each plate I24 and 224 .of the deflecting platepair. In this way the resultant cathode ray spot indication producedupon the luminescent screen-or target I25 0! the cathode ray tube as aresult of the cathode ray beam being projected from the electron gun I26toward the target or screen I25 will be shifted laterally on the targetto represent changes in the point of origin of the signals transmittedfrom the transmitter stations of Fig. 1 relative to the receiving point.

Similarly, the lower deflecting plate pair 324 and 424 will provide forvertical shifting of the spot position in a similar manner under thecontrol of the signals received upon the loops 3M and I. J

In this way a bi-directional trace is produced upon the viewing screenor target I25 of the cathode ray receiver tube by the impacting cathoderay beam or there is produced upon the screen of the cathode rayreceiver tube distinct points or spots of light to represent therelative locations of the several transmitters at the transmittingstation.

Since it is desirable to provide automatic volume control which will beeffective both upon the modulated oscillator or mixer tubes I04 and 204as well as upon the intermediate frequency amplifiers H3 and 2I3 thepotential at the point I23 relative to ground 22I at any instant isapplied to the control electrode I23 of an automatic volume control tubeI21. The automatic volume control tube I21 normally hasits cathodebiased to a value substantially that corresponding to the normal droptaking place across the resistor I22 by suitable bias connected to theconductor or lead I29 which makes connection with the bias source.

The automatic volume control tube I21 is also connected as an oscillatorwith the plate or anode electrode I30 and the No. 3 grid I3I servingtogether with the cathode as the three electrode elements of theoscillator portion. Ac-

cording to this connection and arrangements the anode or plate elementI30 is connected to one terminal of the tank circuit I32 which comprisesthe usual inductance and capacity elements and the No. 3 grid I3I isconnected to one end of a similar tank circuit I33 also comprisinginductance and capacity elements. The tank circuit I33 is coupled to thetank circuit I32 inductively and also by way of the blocking condenserI30. An additional purpose of the condenser I30 will be hereinafterexplained more fully.

Suitable operating potentials for the tube I21 are provided byconnecting a suitable source of anode supply at the terminal point I35and feeding this supply through the resistor I36 to the anode I30. Allhigh frequencies may be bypassed to ground I31 around the anode supplyby way of the condenser I33. Similarly, suitable operating potentialsfor the No. 2 grid I39, serving also substantially as a screen grid, aresupplied from the terminal point I00 through the resistor I 3|.Similarly, high frequencies are bypassed to ground I31 by way of thecondenser In the arrangement herein disclosed it will be seen that bybiasing the cathode I23 to a potential corresponding to the normalpotential obtained at the point I23 the automatic volume control tubeI21 is made sensitive to changes in the current flowing through theresistors I20 and/or 220 tending to change the potential at.

the point I23 relative to ground 22L The oscillator portion of theautomatic volume control tube I21 is, as will be observed, anover-excited oscillator and, accordingly, it is possible in thisarrangement to obtain grid rectification. Furthermore, it will beapparent that the main load on the oscillator is in the tank circuit I33connected with the tube grid element I3I. Accordingly, there isconnected to the tank circuit I33 an additional conductor I03 whichconnects back to bias the No. 3 grids I03, 203 of the modulatedoscillator arrangement I00 and 200, as well as to apply bias to theinner grid of the intermediate frequency amplifiers II3 and M3.

It will be noted in the arrangement shown that a resistor I35 connectedbetween this conductor I03 and ground I31. This resistor I05 serves toprovide a leak connection for the automatic volume control and it ispreferably of a relatively high value, for example, of the order of500,000 ohms. As is now evident from the connections shown the condenserI30 connected between the tank circuits I32 and I33 serves as a blockingcondenser for coupling between the two tank circuits and, in addition,provides for filtering as well. It is preferably of a relatively smallvalue for example of the order of 0.002 microfarad in order to followchanges rapidly.

.If new it is desired to obtain, for example, a more or less relativeindication of the actual distance between the point of reception and thepoint of transmission there may be connected in the lead I and/or 344between the upper end of the leak resistors I45 and/or 345 and the pointof connection of the conductors I44 and/or 344 to the tank circuits I33and/or 333 a damped milliammeter, although this has not been shownspecifically by the drawings and is not in any way essential to theinvention. The purpose of the bias provided on the cathode of theautomatic volume control tube I21 is such that normally this tube isbiased to a cut-ofi value for low values of current flowing through theresistor I22 and then as the current increases through resistor I22there will be applied to the control grid I 3| of the automatic volumecontrol tube I21 a potential increasing in the positive sense which willserve to cause the tube I21 to draw plate current. Consequently, therewill appear and pass beyond the No. 2 grid I39 toward the plate or anodeelectrode I30 an increasing flow of electrons. With the arrangementdisclosed the No. 2 grid I39 serves as a virtual cathode for theoscillator portion of the tube and the increased electron flow will makethe oscillator portion of the tube oscillate still more violently.Accordingly, and from what has been stated above, it will be apparentthat whenever the automatic volume control tube I21 commences tofunction, a very slight change in the potential of the control grid I23relative to the cathode I28 will produce a greatly magnified change inthe potential appearing at the point where conductor M0 connects withthe end of the tank circuit I33. In this way the changed potentialappearing between the tank circuit I33 and the capacity I34 istransferred to act as a biasing potential applied to the modulatedoscillators I03 and 203 as well as upon the intermediate frequencyampliers H3 and 2I3. Hence, the effectiveness of the automatic volumecontrol tube I21 is immediately noted in the intermediate frequencyamplifiers H3 and 2I3 with a result that the current output transferredto the double diode H5 is controlled in an extremely sensi-- tive mannerand the potential effective at the point I 23 relative to ground ismaintained substantially without fluctuation. Nevertheless, thepotential effective upon the opposite deflecting plate electrodes I20and 220 is variable in accordance with the relative strength of thesignals received in the loops II and 20!.

It will be obvious to those skilled in the art that in the use ofultra-high frequency carriers it may be desirable to modulate thecarrier, for example, by a system of the general type disclosed by Fig.3, or by an analogous form of the device, at some frequency to whichtransformers H2 and H3, as well as M2 and 2M and their counterparts forthe assumed channels are responsive. In such a case the modulatedoscillatortubes I03 and 20 i and the intermediate frequency amplifiersH3 and 2I3 would be replaced respectively by a detector and one or morestages of amplification as becomes necessary. Then, the output from thelast stage of amplification (the several stages of amplification beingconsidered equivalent to that shown by the intermediate frequencyamplifiers I I3 and 2 I 3) will be supplied .to the double diode H5, asshown. Also, under automatic volume control tube I21 (connected torespond to signal changes as in Fig. 4) only to the amplifier tubes.Such automatic volume control action may then serve as a bias,preferably on the first stage of the multi-stage amplifler which wouldreplace the intermediate frequency amplifiers H3 and H3. The otherconnections under such conditions may be maintained without anysubstantial alterations from those shown by Fig. 4. v 1

Referring now to Fig. 5, there is illustrated one of several suitablemeans by which the dipoles conventionally represented in Fig. 1 by thenumerals 8, 8' and 9, 9' for transmitting the vertically and-thehorizontally polarized waves may be supported. It has been known in theart and shown, for example, in the book Short Wave WirelessCommunication by Ladner and Stoner, published in 1936 by John Wiley 8:Son, Inc., New York, that the dipole may be positioned within aparabolic reflector and reference may be made to page 420 of theaforesaid publication on this point. According to the arrangementpreferred for use with this invention, thereflecting rods I10 fordirecting the vertically polarized wave may be positioned within asupporting framework I'll, which is usually an insulator and for whichwood has been found to be quite satisfactory. The vertical dipole 8, 8'is positioned at a point very close to the focus of the parabola orslightly nearer the reflecting rods I10 than the true focus point. Inthe preferred embodiment each of the reflecting rods I10 issubstantially one-half wavelength long so that the portion of the,reflecting rod above'and below the insulator support member |'|l issubstantially one-quarter wavelength. The lateral separation between theseveral reflecting rods (indicated as the space H2) is not at allcritical although a one-eighth wavelength separation has been found inpractice to be satisfactory. However, a one-quarter wavelengthseparation of the reflecting rods may be used where desired.

The reflecting rods I for reflecting and directing the horizontallypolarized wave are positioned substantially similar to the verticalreflectors and the vertical dipole except, of course, that thehorizontal reflectors are orientated 90 degrees with respect to thevertical reflectors. The supporting insulating frame I16 for thehorizontal reflectors is preferably formed integrally with supportingframe I'll for the vertical reflectors, although each supporting frameis turned 90 degrees with respect to the other.

The entire transmitter assembly, in view of its compactness and limitednumber of parts as illustrated by way of assembly in two of itspreferred forms by Figs 2 and 3, may be carried within a small containerI18. By the characteristics of the container each transmitteraccordingly may be suitably shielded with respect to each othertransmitter. The several sections or parts of the transmitter areshielded against each other within the container. The entire assembly isthen preferably mounted upon a support so as to be tilted, together withthe radiating dipoles, at a slight angle with respect to the earth'ssurface.

In instances where it is possible to derive more power from thetransmitter than is considered desirable with the arrangement hereinshown, unless the arrangement be overloadedexcessively, it is possibleto radiate the horizontally polarized and the vertically polarizedenergy in two directions, that is, forward and backward of the radiatingelements. In this event the reflectors as herein described and shownmore particularly by Fig. 5 become non-essential to the usefulness ofthis invention and accordingly in order to provide directivity oftransmission it is usually then desirable to provide, instead of thereflectors, suitable director rods positioned in front and in back ofthe radiating dipoles. Such director rods are also known in the art asthe Yagi directors and are disclosed on page 422 of the publication towhich reference was above made. Further, it is also contemplated asbeing within the scope of the present invention to utilize a combinationof the reflectors and the director rods where a more directivetransmission is desired. 1

It should also be understood that with the present invention it is notalways necessary to use two pairs of loops'in receiving but instead onepair of loops may be arranged to provide directional indications in oneplane and a pair of dipoles or quarter-wave antennas "for indications inthe perpendicular plane. In such a case it, of course, naturally followsthat a single dipole only is used at each point 2 through 1 of thetransmitter, with the choice between a horizontal and vertical radiatingdipole being determined in accordance with the choice made at thereceiver for the use of loops to select either horizontal or verticalindications.

While the invention herein set forth has been described in some of itspreferred embodiments it is, of course, apparent that many changes andmodifications of that disclosure may be made without departing from thespirit or the scope of the invention and accordingly itis believed thatsuch changes and modifications may be made provided they follow fairlywithin the scope of the claims hereinafter appended.

What I claim is:

1. In a navigation system, a plurality of transmitters located atpredetermined positions relative to a significant area, each of saidtransmitters being arranged to radiate simultaneously...

both horizontally and vertically polarized radiant energy, means forrendering the several transmitters of the plurality sequentiallyoperative in a predetermined order, means for receiving simultaneouslythe instantaneously transmitted vertically and horizontally polarizedradiant energies. means for separately amplifying each of thesimultaneously received signals, a cathode ray indicating device havinga beam developing means and a plurality of beam deflecting means fordeflecting the developed beam, and means for separately energizing thedeflecting means under the control of each of the simultaneouslyreceived signals so that the developed beam is deflected inbi-directional paths to indicate the point of signal origination.

2. In a receiving system for receiving from a signal source, a pluralityof directional receiving means, a plurality of similar amplifying means,means for energizing each of the separate amplifying means independentlyof the other with signals variable in accordance with the effectivedisplacement of the directional receiving means from a predeterminednormal position relative to the signal source, an electronic rayindicating device having included therein a means to develop an electronbeam, a plurality of differentially active deflecting means fordefleeting the beam, means for energizing the deflecting meansindependently from the signal in each amplifying channel, and means forcontrolbeam developing means deflecting means under the control ling thesignal level in each independent amplifier in accordance with acomparison of the instantaneous total signal level of each channelcombined as varying from a predetermined normal level.

3. In a navigation system, a plurality of transmitters located atpredetermined positions relative to a significant area, each of saidtransmitters being arranged to radiate both horizontally and verticallypolarized radiant energy, means for rendering the several transmittersof the plurality sequentially operative in a predetermined order, meansfor receiving simultaneously the vertically and thehorizontallypolarized radiant energy, means for separately amplifyingeach of the simultaneously received signals, a cathode ray indicatingdevice having a beam developing means and a plurality of beam deflectingmeans for deflecting the developed beam, means for separately energizingthe deflecting means under the control of each of the reecived signalsso that the developed beam is deflected in bi-directional paths toindicate the points of signal origination, and means for maintaining thesignal level in each amplifying means at a level controlled inaccordance with variances from a predetermined normal total combinedsignal response.

4. In a navigation system a plurality of transmitters located atpredetermined positions relative to a significant region, each of saidtransmitters being arranged to radiate both horizontally and verticallypolarized radiant energy of.like frequency, means for rendering theseveral transmitters of the plurality sequentially and individuallyoperative in a predetermined order, a plurality of directionallyresponsive means each for receiving independently of the othersimultaneously the vertically and the horizontally polarized radiantenergy, means for separately amplifying the received radiated signalsfrom each of the directionally responsive means for each of thepolarized transmissions, a cathode ray indicating device having a beamdeveloping means and a plurality of beam deflecting means for deflectingthe developed beam, means for separately energizing the deflecting meansthe separate received signals so that the developed beam is deflected inbi-directional paths under control of the variance of signal strength.in each of the separate amplifying means to'indicate in accordance withvariances from a predetermined normal the point of signal origination.

5. The system claimed in the preceding claim comprising, in addition,means for individually biasing the plurality of amplifying means forreceiving the polarized transmissions under the control of variancesfrom a predetermined normal level of combined signal strength from eachseparate amplifier.

6. In a navigation system, a plurality of transmitters located atpredetermined positions relative to a significant area, each of saidtransmitters being arranged to radiate both horizontally and verticallypolarized radiant energy signals, means for rendering the severaltransmitters of the plurality sequentially operative at a predeterminedrate, means for directionally receiving simultaneously two directionalversions of each of the instantaneously transmitted vertical andhorizontal polarized radiated energies, means for separately amplifyingeach of the received signals, a cathode ray indicating device having aand a plurality of beam for. deflecting the developed for separatelyenergizing the deflecting means beam, and means under the control oftally and vertically of each of the that the developed beam is toindicate the received signals so deflected in bi-directional paths pointof signal origination.

'7. A navigation method comprising the steps oi transmittinghorizontally and vertically p0-' larized radiant energy signals from aplurality of points located at predetermined positions relative to asignificant area, rendering the transmissions from the several pointssequentially operative in a predetermined order, receivingsimultaneousiy the instantaneously transmitted vertical and horizontalpolarized radiant energy,sep-, arately amplifying each of the receivedsignals, developing electronic energy for producing visible pointindications simulating in perspective the point sources of signal energyand controlling the position of the point indications under thedifierential control of the amplified received signals.

8. In a navigation system, a plurality of transmitters locatedat'predetermined positions relative to a significant area, each of saidtransmitters being arranged to radiate both horizontally and verticallypolarized radiant energy signals,

means for rendering the several transmitters of the pluralitysequentially operative in a predetermined order, means ior receivingsimultaneously the vertically and the horizontally polarized radiantenergy, means for separately amplifying each of the received signals, acathode ray indicating device having a beam developing means and aplurality of beam deflecting means for deflecting the developed beam,means for separately energizing the deflecting means under the controlof the received signals so that the developed beam is deflected inbi-directional paths to indicate in substantially perspectiverelationship the several points of signal origination.

9. A navigation method comprising the steps of transmitting horizontallyand vertically polarized radiant energy signals of like frequency from aplurality of points located at predetermined positions relative to asignificant area, rendering the transmissions from the several pointssequentially operative in a predetermined order at a predeterminedswitching frequency, receiving simultaneously the instantaneouslytransmitted vertically and horizontally polarized radiant energy,independently amplifying the received energy for each of the receivedhorizonpolarized signals, developing electronic energy for producingvisible point indications simultaneously in perspective relationshipwith respect to the point sources of signal energy and controlling underthe differential control of the amplified received signals the positionat which the visible points are made observable.

10. A navigation method comprising the steps of transmittinghorizontally and vertically polarized signal energy of like frequencyfrom a plurality of points located at predetermined positions relativeto a significant area, rendering the transmissions from the severalpoints sequentially operative in a predetermined order at a verticallyand horizontally polarized ener y, developing a cathode ray beam forproducing visible point indications upon a target area to represent inperspective the points of origin of the separate ode ray beam to producea plurality of light point sources of signal energy and controllingunder indications on the viewing target spaced in verof significantpoints arranged in a'predetermined determined normal total strength 01.each of the location relative to a significant region verticallyindependent Signal p fica 10 and horizontally polarized signal energy oflike 14. In a direction indicator for receiving transl frequency fromeach point, switching the transmitted polarized radiant energy waveswhich missions from one to another of the radiating represent horizontaland vertical components of points in a predetermined sequence at ai'repolarization oi radiant energy originating from a lfi m-r t at afrequency at which persistence determined repetition frequency, acathode ray l and horizontally polarized signal energy 01' like to thereceiving means of the energy radiating 13. A method of aerialnavigation which com Versions 01' the said received energy, means forfrequency from each point, switching the transcomponent of polarizationof the received radiant order that the vision persistence phenomenon forenergizing the beam deflecting means in acreceived at each point,producing a cathode ray the targetisaid light point indicationsrepresentm a viewing target, dlflerentially comparing the means of theradiant energy transmitting means. unplifled output signals for eachreceived signal at like polarization, deflecting the produced cath-ROSCOE H. GEORGE.

